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9GEOG landscapes and water
Form and Process
16
Geography
Undergraduate 1
04/05/2010

Additional Geography Flashcards

 


 

Cards

Term
what is the longitudinal profile of a river?
Definition
a smoothly decaying curve, with steep slopes found in the headwater and low slopes found at the mouth where a river empties into a body of still water
Term
what is the baselevel?
Definition

the lowest elevation on the channel, the elevation that the river cannot erode below

 

for many rivers this is sea level but there are cases where sea level is not the baselevel (ex: lakes and regions with no external drainage to the ocean in which playas (dry lakes) provide the baelevel)

Term
what is a graded river?
Definition

a river long profile with a smoothly declinging slope

 

the channel has adjusted its gradient to the baselevel

 

viewed as a sort of equilibrium profile

 

bumps and hollows in a river profile = transient features that call for explanation

Term
how steep will a bedrock section be?
Definition
bedrock is more resistant to erosion so it will be steeper (more shear stress required to erode it, hence steeper slope)
Term
how will debris affect slope?
Definition
it will build a step that steepens the profile (and can also create lakes)
Term
where will displaements occur in a river and how will they affect the river?
Definition
they occur along a fault crossed by a river and are manifested in the long profile. if the upstream side moves up relative to the downstream side, a convexity will be seen in the profile. the opposite case (upstream side moves down relative to downstream side) is likely to be erased quickly by deposition of sediment
Term
what are knickpoints?
Definition

short steep sections in a river channel created by resistant rock types or baselevel lowering

 

they migrate up the channel over time as the river works to produce a smooth profile

 

waterfalls are knickpoints, usually produced by a layer of erosion resistant rock

Term
what dictates the downstream variations in grainsize of bed material?
Definition

changes in slope

 

on the steepest slopes, the basal shear stress is highest, and all but the largest grains are entrained and moved downstream. as the slope decreases downstream, the shear stress available to entrain sediment declines, and so does the size of the bed material

Term
why does the water in a meandering channel continue in a more or less straight line even as the channel bends?
Definition

momentum

 

it sends the water against the outer edge of a bend

 

the water then belatedly makes the corner, rebounding off the wall and flowing down the water surface slope created by piling up

 

the resulting water flow pattern forms several helical rolls within the channel

Term
where do water depth, velocity, and shear stress tend to be greatest?
Definition
on the outside corner of a meander bed
Term
what is the cut bank?
Definition
the bank of the outer edge of a bend, where erosion is concentrated
Term
what is the point bar?
Definition
where sediment is deposited on the inner edge of the bend, a region of shallow flow and low shear stress
Term
what is an oxbow lake?
Definition
where a meander loop has become too long, a flood occurs, and the river finds the shortcut and cuts off one of the loops. this abandoned loop becomes an oxbow lake and slowly fills with sediment over time
Term
what happens when flow spills out onto a floodplain and what is an overbank deposit?
Definition

the sediment concentration in a river channel decreases the higher the flow, and the grain size decreases as well. it is this finer grained sediment that is carried out of the channel and onto the flood plain.

 

overbank deposits (sediment deposited by a river outside the channel) are always finer grained than the sediment deposited in the channel

 

deposits closest to the channel tend to be coarser than the sediment deposited further out on the floodplain

 

Term
what is the natural levee
Definition
a ridge of sandy material often found along channels
Term
why do farmers like to plant in floodplains?
Definition
flat land with available water and perfect texture for agriculture (fine deposits that wash up during flooding)
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